I have had vaginal bleeding for about three weeks now, it's pretty light but constant. it started as brown discharge and severe pain in my lower left ?

Get checked. : You should get checked, if not by your ob-gyn then by an emergency department doc able to perform ultrasound. You need to make sure the ovary isn't twisted around, or a fertilized egg isn't implanting in the wrong place.

Needs evaluation: What you have is not normal, the pain and abnormal bleeding is worrisome.You need to see your obgyn as he or she can do an exam, blood work to r/o various conditions like pregnancy or ectopic pregnancy and an ultrasound. Once those are done you can be treated appropriately. Your problems have gone on too long, i would get in asap or go to the er if you cannot see a doctor.